1. Field of the Invention
The present invention relates to a gravity or pressure filter assembly that includes underdrain laterals and a bed of granular filter media. More particularly, the present invention relates to an underdrain flume plate used during installation to prevent grout from entering the flume.
2. Description of Related Art
Typical gravity or pressure filters use some type of filter media that captures the dirt particles from a liquid being filtered as the liquid passes through the media to an underdrain or collection system. Generally, beneath the filter media is a series of underdrain laterals consisting of underdrain laterals that are attached to the filter floor using a series of anchor rods, struts, and grouting. Such a filter may also have a flume, a deeper channel set into the floor of the filter through which backwash fluid and, optionally, air may be introduced into the filter. The underdrain laterals placed over the flume must therefore be in fluid communication with the flume to allow the backwash fluid to pass up through the underdrain laterals and the filter media. This is accomplished by the placement of openings in at least one of the underdrain blocks which make up the underdrain lateral. The underdrain blocks containing this opening are commonly referred to as flume blocks. The flume may be located on the front end of the filter or somewhere in the middle.
When installing a gravity filter, anchor rods placed in a grid pattern are firmly attached to the floor of the filter and struts are attached to the anchor rods to form a grid pattern on which the underdrain laterals sit. Grout is placed on the floor of the filter to fill in any space between the bottom of the underdrain lateral and the filter floor. However, it is necessary to keep the grout from running into the flume during installation of the underdrain laterals. A piece of bridging, a formed plastic trough, is used to hold grout or caulking against the bottom edge of the underdrain lateral to create the seal around the flume opening. The bridging must be pulled tight against the underdrain lateral and held in place with wire until the grout sets. It must also sit on some base grout to seal the bottom of the bridging to the filter floor. If the flume area is accessible, a worker enters the flume and pushes up on the bridging to ensure a good seal after the bridging has been wired to the underdrain lateral. This process is time consuming, messy, and often the effectiveness is less than desired as grout is able to leak into the flume.